Method of and means for rectifying the scale and perspective of a picture



Dem 2?, 1927.-

E. H. CORLETT ET AL METHOD OF AND MEANS-FOR RECTIFYING THE SCALE AND PERSPECTIVE OF A PICTURE Filed; May 1920 4 Sheets-Sheet 1 Dec. 27, 1927. 1,654,070

. E. H. CORL'ETT ET AL METHOD OF AND MEANS FOR RECTIFYING THE SCALE AND PERSPECTIVE OF A PICTURE Filed y 1930 h 4 Sheets-Sheet 2 [2 00411 f1 60am)?" Dec. 27, 1927.

E. H. CORLETT ETAL METHOD OF AND MEANS FOR RECTIFYING THE SCALE AND PERSPECTIVE OF A PICTURE Filed May D 4 Sheets-Sheet 3 wfi w, ZHN mi .6 a M M A: @Z w 5 4 M W 6 M ,1 2 M 5 4/ m m Dec. 27, 1927. 1,654,070 E. H. CORLETT ET AL METHOD OF AND MEANS FOR .RECTIFYING THE SCALE AND PERSPECTIVE OF A PICTURE Filed May 14, 1920 4 Sheets-Sheet 4 XZT 4 *1 Xi 1" :1 h m MW w 24 30 V 26 30 K x 35 x I hatent'edDecaZZIQZ'I.

UNITED STATES PATENT OFFICE.

' EDWIN H. CORLETT AND MAX w. AENETT, or CLEVELAND, "01:10.

mnrnon or AND MEAns, Eon REGTIFYING THE SCALE AND PERSPECTIVE or I IICTUZRE.

' Application filed ma 14, 1929. Serial mi. 381,402.

Our invention relates both to the method ofand the means for rectifying perspective in pictures.

We believe we are familiar with prior '5 practice and publications pertaining to this art, and are of the opinion that prior elforts and suggestions, while involving a movable support for the picture, did not enable adjustment of the picture in. the manner we to shall disclose. We propose mounting the picture object, or representation containing elements of perspective on a support or easel adapted for ,con'ii'iound, indeed for universal I turning motion in such a way that one point in in the picture constantly remains substantially fixed. The drawings exemplify practice of our invention by rephoto'graphing an aerophotograph having elements of perspective in consequence of a tilt or dip of' the aircraft at the moment of exposure," In re-, photographing, the point of the vphotograph which remains substantially fixed during the angular adjustment'of' the picture preferably lies in the axis of'the lens to be used for projecting the image to be rephotographed. If the angle at which the aerial photograph was taken is known, as it may be by use of the Method of andap- 'paratus for effecting optical projections patented by Edwin H. Corlett May 3, 1927, No. 1,626,787; the desired result by re photographing can be obtained by mounting the negative of the aerophotograph at an angle, calculated from the known angle, to the plane of the new negative, because it completes the list of known factors required in the computing equation. The other lrnown factors are the focal length of the lens of the taking camera, the focal length of the lens in the reducing camera and the ratio of enlargement or reduction required. Til the angle at which the aerophotograp-h was taken is not known the use of another feature of our invention becomes necessary and such feature is based upon another discovery, namely, that while'three points de termine the position of a plane they cannot determine the angularity or tilt of the plane because a triangular figure does not definitely reveal perspective without the possibility of two solutions where there is perspective. That is to say, a triangular plane lid , mfay be tilted in either one of two opposite directions with the same effect to the eye and it is therefore impossible for the eye to transmit accurate intelligence of the elements of perspective because the image can appear the same. In short, projection of three points is not a true test for ascertaining the component angles (or the resultant solid angle) together with the directions of each, with respect to any given plane, which, at the moment of recordation,'angularly relate the recording apparatus to the given plane. Consonantly, our invention comprehends the employment of a definitely dimensioned control figure including four or more points which have a definite relation to each other. Such figure is to be drawn upon a transparent surface and so as to be free from perspective -and should be considered as having been laid out from survey data such that its corner points represent features or selected'p oints identifiable on the print or negative. Such control figure is to be used as a standard for comparison and will serve a similar functionas the ground glass commonly used at thebach of a camera to enable adjustment to proper focus. Moreover, the control figure includes two diagonal lines extending between different pairs of the corners so that the point of intersection of such lines may bev brought into line with the center of the lens'and with the fixed] point in the surface of the picture to ments, namely, the picture, the lens and the control figure may be fixed whereas the other two should be novable. As finally adjust: ed the point of. intersection cf the two crossed'lines on the, control figure and the fixed point in the surfaceofthe picture both lie in the axis of the lens. It is helpful. but notessential that the two crossed lines on another preliminary control figure-be projected to coincide with lines drawn on 'the easel which supports the picture and which lines would, it continued, cross each other on the image of the icture, l Theearl'iest andtoday t e most frequent attempts made'tc correct by rephotograplr ing aerophotos, taken at an angle with the horizontal, all hinge upon the misconception that such correction can be accomplished by be photographed. Any one of the three ele-' i introducing a swinging back on a camera in the studio or by providing for universal motion on the easel itself. In other words, attempts made to rephotograph a picture, in error due to perspective, from a point lying in the plane determined by the vertical through the lens and the axis of the lens and on the opposite side of the axis from the image of the vertical point cannot correct such picture. This method may eliminate perspective, but the resulting picture will be distorted to the extent that linesat ninety degrees on the ground will be shown, excepting for one directional position of those lines, at .an angle other than ninety degrees. It is the purpose of our invention to correct perspective only, rather than perspective and distortion, excepting in one special arrangement which is illustrated in Figure XXII, relying upon other means for correction of the secondary error.

tAn Austrian army ofiicer, Scheimpfiug, in order to reduce to one plane photographs taken by a multiple camera of his design,

produced a reducing camera which corrects for perspective and leaves no secondary error when the direction and amount of deviation from the plane is known. This instrument has been called a perspectograph. The cor-' rected picture cannot be produced to scale from the original. Its scale is a function of the angle of inclination and the focal length of the. reducing lens, as well as the focal length of the taking lens and its location with respect to the object photographed.

For description of this apparatus we refer,

to Military Topo raphy and Photography by Floyd Oarloelg U. S. Army; and, to an article by F. H. Moflit, in Engineering- News-Record, Ma 22, 1919. The theory of this apparatus, w ile simple, is lengthy and is out of place here.

Having knowledge of the direction, amount of tilt and altitude or true location of four points, we claim that our apparatus will correct perspective to any scale from the distorted negative or print to give a print or negative of such a nature that subsequent enlargement in one direction will give a true and uniform scale picture.

To construct a map from aerophotographs 1t 1s necessary to reduce or enlarge the original photographs to the scale desired and also to apply a correction for distortion of perspective due to the photographs having been taken with the axis of the lens at angles varying from a true perpendicular. For the purpose of making a correction of this distortion the following device has been made and used by us:

1. An outer supporting frame.

2. A circular inner frame rotating within the supporting frame.

3. A swinging inner frame, the axls of which is on the plane of the circular frame.

of which is at right angles with the axis of the swinging inner frame and the center of which remains constantly on the plane and in the center of the circular inner frame. Instead of being perpendicular to each other, the axes of the easel could form any angles greater than zero. I

It has been assumed that if the actual relation between three or more points shown upon the photograph were known that the photograph could be placed upon the above described easel and so manipulated that a re-photograph could be taken which would be correct in perspective and to the scale desired. It was discovered by experimentation that if only three points of control were used that there were two positions of adjustment which would give the desired coincidence of points, but only one position which would give a proper correction of perspective. This indicated the necessity of at least four points of control for the purpose of correction. When using four points there is only one adpistinent which Wlll avold the chance of error.

Adverting to the four sheets of drawing:

Figures I to VII inclusive, are various diagrammatic views, to be considered in order as a graphical explanation of our invention.

Figure VIII is a diagrammatic view showing the plane of an aero film parallel with the horizon or with the mean plane of the terrain image in the field of view.

Figure IX represents a picture of an allotment taken with the camera in the position shown in Figure VIII.

Figure X is a view corresponding to Figure VIII showing in full and dotted lines two aero cameras inclined in different direcwhen the angle at which the photograph was taken either is or is not known, and consists in obtaining a negative free from perspective by rephotographing the print having elements of perspective, the print bein held at the angle to the plane of the negative.

Figure XIII is an enlarged plan view of a control figure detail.

Figure XIV is an enlarged view of an-' other control figure detail.

Figure XV is an enlarged front elevation of a universal motion fixed point easel such as is shown employed in Figure XII.

Fi ure XVI is a vertical Section on line XV XVI of Figure XV.

Figure XVII is a section on line XVII- XVII of Figure XV.

Figure XVIII is a still further enlarged XII showing a modified method of obtaining llti Eli

section taken on line XVIIL-XVIII of Figure XV. i

Figure XIX is an enlargement of a section taken on line XIX--XIX of Fig-j ure XV. I

Figure'XX 1s a diagrammatic View partly corresponding 1n arrangement to Figure a print tree from perspective, by projecting the representation on the negative having the elements 0t perspective, to a sensitized suratace at an angle to the plane of the negative. Figure XXI is a diagrammatic view of a supposed square terrain image.

Figure XXII is a diagrammatic view illustratin how change in the focal length of a'lens aFects the functioning thereof during the adaptation of our method.

In Figure I, ABGD is an aerophoto, upon which points efg'h are known in their relation to each other by virtue of survey or previous aerophoto. P isthe image of the point on the terrain directly over which ABUD was taken; and U is the center of the 0d. Ubviously, if ahcal can be rephoto graphed so as to appear as a square, all

points in the picture in which abaal lies will be thereby corrected for perspective.- It is our purpose to show that abcd can be rephotographed into a rectangle, with. sides aol and be longer than sides'ab and cal, to be a subject for further simple correction.

In Figure III, it abccl be so rephotographed as to keep the perpendicular to Mill and to the drawing sheet at U parallel to the plane of the lens and the point V lying in the plane cit-the lens, the image of abort will be Fill a rectangle. This follows because planes de termined by ab and L and Orland L respectively, whichplanes intersect in line LVcut parallel traces'on the sensitized plane not shown, which --'s'parallel to the plane of the lens; and the p hes determined by ad and L and Z and L respectively cut traces on the same sensitized plane parallel to each other and perpendicular to the traces of the planes determined by'abL; and col L because the intersection of the planes ab L and 0d 'L is at 90 with the intersection ofthe planes ad L and a?) L. It is'further obvious that the images of ad and will be equal to each other, and greater than. the images ab and ad, which will also. be {equal to each other. To demonstrate the latter-part of the last as- Sell/1011:

clination such that the axis of the lens passes through 0, the angle bOc will be photographed in to an angle larger than itself, as bOc in Figure V islarger than 5-O0' in Figure IV.

Now, if angle aOcZ, Figure V, be rephotographed under conditions as specified inthe second precedingparagraplnit Wlll enlarge into angle aO'ol, Figure VI.

Angle (aOcZ) Figure IV equals angle (dOc) Figure IV, because a'bod is a h i Bil square.

Angle (bO'c') Figure V is greater than angle (b'Oc) Figure IV. The preceding statements are made to show that a hypothetical square (Figure IV), whose axis (not diagonal) is the lineMN, though aero photographed into a trapezium (Figure V), may be corrected into the rectangle shown in Figure VI. v

Angle (aU'd'y Figure V equals angle (E'Uo") Figure V.

Figure VI is a part of an acre photograph from which horizontal perspective has been eliminated and in which two systems of scales exist different from each other, but separately uniform. I

Angle (aUcZ) Figure VI is greater than angle (a'UcZ) Figure V, therefore angle aUol Figure VI is greater than any angle 1n the original square; and so ad' Figure,

V1 is greater than ab Figure VI.

Angle (ad) LU equals angle (50) LU. There are two ways in which the above theory may be applied. It we lrnow the dis tance UP, and the focal length 'ot thelens of the aero camera, and ad Figure VI or ba Figure VI, the angle VUL and the distance ldft ice 7 UL may be n'lathematically solvable loy lrnownjmethods of solid geometryand trigo- 1 nometry. Ur, it we know the true di1nensions of the figure ef h, the picture ABCD may be so manipulated by cut and try meth ods that it may be'located' so that a change of dimension of the image of efgh in one direction only will make it similar to, the original efgh (within the limit that UV does not too closely approach UL)-out oi consideration of conditions 03E practical photo raphy so placed, the conditions of lines 13 et seq.

page 7 are fulfilled and perspective is-elim inated, leaving only a uniform dlstortlon .1n

any desired and practical extentwill result in the rephotographed image of afghi being true to any dimension desired in either of involving depth of focus. When A CD is two irections, namely, direction parallel to ab Figure VI' or ad Fig; VI.

' In order to accomplish thisgmanipulatlon otP BCD either as a negative or as aiprint,

* the design of Fig. VII is submitted, being a device which might be used. E is a frame, approximately parallel to the plane of the lens. F'is a turntable, rolling on three or more points iclmn. G is a carriage mounted on axes S and T. H is the plate or easel, mounted on G, by axes Q and R. The construction is such that Q, and R lie in the plane of the surface of H, and further that Q, and R and S and T all lie in one plane, regardless of how H may be tipped or turned, and that Q, and R and S and T intersect in a point 0 on the surface of H, and that point (J is the center of rotation of F. By this construction, H potentially has a universal motion about thefixed point To refer to Figures I and II, if OP is known, (always assuming in such a case that the focal lengths of all optical elements, as

well as the scale of the finished product are known), the photograph (print or negative) is so mounted that O coincides with point 0 on H, Figure VII and OM coincides with either Q,-R or S T, Figure VII. Then motion about one axis, of a calculated amount, supplies the required correction.

The line lying in the aero photo and perpendicular to MN at O and all lines parallel thereto are separately uniform in scale,

whereas all lines parallel to MN separately vary in scale. If OP is not known,

and the polygon efgh is, the photograph (print or negative) is so mounted that the intersection of the diagonals of efgh preferably coincide with point 0 on H, Figure VII. Then manipulation will determine a position for H such that the image of efglz. will require correction only in one dimension in order that it may be similar to efgla, Whether a negative or print of it is used on H, the resulting image, in either case, will be free from perspective.

Referring next to Figure VIII, an aero camera 1 is there shown to have the plane 2 of its film parallel with the horizon and therefore substantially parallel with the terrain image 3 in the field of view of the lens of the camera. According to Figure VIII it is to be assumed that the terrain image is a portion of an urban allotment of which the' four far corners of four blocks happen to prescribe a rectangle. I have designated such four corners with the reference characters a, b, 0, (Z toconform with the reference letters on Figure II. It will be observed also, that diagonal lines extending between a and c and b and 03 respectively intersect at'the point marked 0. The picture shown in Figure IX is furthermore to be assumed as free from elements of horizontal perspec-- I tive hereinafter called simply perspective.

Figure X shows the aero camera 1 in two different tilted positions with reference to the terrain level, the angle of tilt of one of the cameras appearing in full lines and of the other in dotted lines and being indicated by the planes 4- and 5 of their sensitized surfaces respectively. The picture taken with the camera 1 tilted as shown in full lines in Figure X should be considered the same as the picture shown in Figure IX with elements of perspective introduced. It is these elements of perspective, which our invention will correct.

Directing attention to Figure XII, which is a diagrammatic illustration showing how elements of perspective, the mathematical Values of which are unknown, may be otherwise taken care of. A lens (3 is supported by a bellows 7, the function of which is to permit of linear adjustment of the lens along its own axis. T o the rear frame of the bellows a compartment 8 is detachably fitted at what may be considered the plane 9 of the camera back. Mounted in any suitable manner in the plane 9 (not shown, because old practice for which nothing herein claimed) is a transparent member 10 upon which is drawn what we term a control figure, clearly shown in Figure XIII. This figure must include a plurality of sides to contain, as exemplified, four points 11, 12, 13 and 11 which may be considered the equivalent in function of the four corners a, Z), c and d twice before referred to. While the four sided figure happens to be a square it need not necessarily be so, because any polygonal figure of more than two sides will answer. Connecting the corners 11 and 13 is a diagonal line 15, while connecting the corners 12 and 14; is a diagonal line 16 which crosses the line 15 at a point 17. The manner of use of this control figure will be later explained. The back of the compartment 8 is provided on its inside with a reflector 18 ahead of which a lamp 19 is mounted so that it intersects the axis of the lens 6. It is to be understood that after the control figure on the sheet 10 has served. its purpose of enabling proper adjustment to be made, a sensitized surface will be substituted in its place or in the focal plane of the lens 6.

A suitabledistance removed from, so as to intersect the angle of View of the lens 6, is a support 20 for the picture or photograph which support is preferably set up substantially perpendicular to the axis of the lens. Thus the optical element 6, the object and an element for receiving the representation or image of said object are arranged along an optical trail. IVhile the construction of the support for the easel which is in turn to support the picture or photograph with the ele- .ments of perspective appears in Figure XII,

(ill

net tom ioned with tour equispaced recesses 22, pairs of which are dian'ietrically opposed to perpendicular lines. In each of the recesses 22 is mounted a ball castor, the balls 23 of which project into the annular depression 24L formed in the rim of a turntable 25 which latter is thus rotatably mounted. The turntable 25 is pror'ided at its center with a square aperture 26 in which a counterweight ed frame 27 is mounted for adjustment move ment in the following described manner. Assuming the support 20 and therefore the turntable 25 as being in a substantially vertical position. the middle of the top and bot tom edges of the aperture 26 carry periorated angle irons 28, while opposed to these and attached in any approved manner to the upper and lower sides of the frame 27, are another pair of angle irons 29. Adjusting screws 30 arev passed through the two pair. of angle irons and are then locked in any desired position by means of a pair of milled nuts 31. By means of this connection between the turntable 25 and the frame 27 the up and down position of the frame may be determined, whereas the frame as a whole being swung upon two vertically disposed axes enables it to be turned thereupon at an angle to the plane of the turntable 25.

lt lountcd for movement in a rectangular aperture in the frame 27 we provide what may be termed an easel 33. Such counterweighte'd easel we have elected to mount on horizontal axes in a manner like the "frame 27 is mounted on vertical axes in the aperlure 26 of the turntable 25. Figure XVIII discloses the details of such mounting to in elude two pairs of juxtaposed angle irons 3 and secured to opposite sides of the frame 27 and easel 33 respectively. Screws 36 are then operatively passed through both angles and provided with lock nuts 37 for a wellknown purpose. Thus the easel 33 is adapted for swinging movement about a horizontal axis and is capable of being fixed at any desired angle. The whole structural arrangement will thus be seen to enable imparting of a universal turning motion to the easel and therefore to any target or image supported thereby. As will be observed upon inspection of Figures XVI and XVII, two of the axes oi? turning movement of the easel, namely, that axis prescribed by the pair of alined screws 30 and that axis prescribed by the pair of alined screws 36 lie within the plane of the easel 33. larri'ed along opposite sides 01 the ease] are a pair of rollers 38 and 39 provided with knurled handles 40 and 41 respectively, by means of which an indeterminate series of films may be successively brought into position in front of the easel. According to the method practiced with the apparatus shown in Figure hill, the print from a photographic negative is to be attached to the front of the easel to constitute during the second or last stage the object for the lens 6, and the disposition ol such print will be such that its image will contain a point l2 which will constantly re main fixed during any movement which may be imparted to the easel 33 and therei ore to the picture mounted thereon.

Considering the lens ta, its local plane at the back ol: the camera (whether occupied by the sheet 10 or a sensitised surface) and the representation or image which includes the point l2 as three elements, any one ol the three may be initially lined the other two adjusted to obtain the desired result or angular relation oi? three planes, namely, the plane of the lens, the focal plane oi the lens and the plane of the representation to be rephotographed. Either ol the last two planes could be construed to be the focal plane of the lens, but, of course, only one coincides with the back ot the camera, whereas the planes are to be at conjugate distances from the lens. It is helpful, though not essential, to first use a ground glass d3 shown in Figure XIV marked with lines ll and which cross each other at right angles at a point 46. Such glass ll-3 is to be used in the same place and in the same man nor as the sheet 10 by temporarily mount ing the same at the baclr ol the camera.

The apparatus shown in Figure XII may be a reducing camera which is to be used in the following manner. The center 46 on the ground glass 43, as in all cameras, is to be on the axis of the lens 6. The fined point 42 is also preferably on the axis of lens 6. This is not essential because alter various trials and attendant dificulties compensation for its misplacement could he made. Assuming the easel 33 to be in its vertical position and the glass 43 at the baclt of the camera, the light of lamp 19 will then project a clear image of the lines lland 4-5 on the easel, following which the easel support is to be so adjusted as to bring the center of the lens, the point l6 and the point 42 into line. This is the more easily accomp'li shed if the line 45 is made to coincide with the imaginary line through the screws 30, and the line 44 with the imaginary line through the screws 36. Next, the control. sheet oi paper or cloth 10 is substituted in place of the glass l3, whereupon its figure, including the points ll to i l inclusive and the lines 15 and 16 are projected as a clear image on the print. Then the easel 33 is so adjusted as to bring the projected images of the tour points II to 1stinclusive into a position with respect to the tour identifiable points on the print, which may be assumed as efg/L Figure l, of which the designated points 11, 12, 13 and 14 may mark the conventional figure shown in Figure XIII, (presumably tilted) that while in such position the projections of the four points 11 to Ill) llll

14 inclusive will occupy positions on the print such that While the resultant figure will not be the same as that formed by the identifiable points on the print on the control sheet, such project l figure will be of a nature that a uniform linear expansion or contraction of it along-one dimension will reproduce substantial superimposition of the projected control points onto the actually identifiable points. Change of dimension in only one direction is subsequently required. A cessation of adjustment movement of the easel 33 will occur when a test either by inspection or measurement, as commonly practiced in the art, shows that a simple uniform enlargement or reduction, with or without a proportional additional change of dimension along a certain set of parallel lines, will produce the sought for result. In other words, adjustment movement of the easel 33 ceases when, what we shall call a parallelographic projection of the control figure is obtained on the print. A plane geometric figure determined by four points may, when optically projected and after adjustment of I the' optical apparatus so as to shift the four points uniformly in directions parallel with two determinable angularly related lines. be made an orthographic projection with four points determining another geometric plane figure. That is what we mean byparallelographic projection. That any projection is readily altered is well known. For example, while a square, in the hereinbefore described methods, always projects into a parallelogram a suitable lens can reproject a parallelogram into a square.

After having obtained a desired projection of the representation on the sheet 10 on the print which is supported on the easel, a sensitized surface is in turn to be substituted in place of the control sheet 10 and rephotographing accomplished, by satisfactory illumination of the print on the easel 33.

It is common knowledge that a perspective representation on one plane of 91. sets of parallel lines within another plane comprises merely n sets of lines radial to n points along a line in that first plane; commonly called the horizon line. While it is the reversal of the order of representation that within a plane and are substantially radial to a plurality of points scattered along a line, as a plurality of sets of substantially parallel lines lying within another plane and the optical transference of data respecting such lines in the first mentioned plane to the second' plane in such a manner that a plurality of points in the first plane bear to a corresponding number of points in the second plane a substantially mathematically con- -tinuous relation whereby a change of dimension of the plane figure determined by the first mentioned points so transferred, proportionately in two angularly related directions, produces substantial coincidence of the transferred points with the points on the second plane.

The modification to which Figure XX. appertains, besides being photographic apparatus, is in a sense the reversal of the arrangement shown in Figure XII. The difference betwen Figure XII and Figure XX is clearly designated on the drawing. The one is a method of obtaining a negative free from perspective and the other is a method of obtaining a print free from perspective. A compartment or chamber 47 closed in front by, a bellows which supports the lens 48 contains a lamp 49 set in the axis ofthe lens and ahead of a reflecting surface 50. Separated from the compartment 47 is a suitable support 51 upon which is mounted an easel 52 which is to be presumed as capable of angular and linear adjustment and which is also to be considered as corresponding to the back of the commonly used camera. It is to be furthermore presumed that either a control sheet or a ground glass, such as are shown in Figures XIII and XIV respectively, may be movably supported upon the easel 52 preparatory to final substitution therefor of any reproducing surface, preferably photo-sensitizcd paper. Set up within the compartment 47, between the lens 48 and lamp 49, is a universally movable easel construction. precisely like that shown in Figure XII and including the support 20, turntable 25, frame 27 and easel 33. The arrangement shown in Figure XX is intended to project the image of a negative having elements of perspective to a sensitized surface held at an angle to the negative, the adjustment of the angle of the latter to yield a value which shall be a function of that of the known angle at which the negative was exposed as well as of other determinants being accomplished as heretofore described, after which the image on the tilted negative will be projected upon the new sensitized surface. WVhile the control figure is not absolutely essential in practising our invention according to the illustration of Figure XX with knowledge of the angle at which the picture was taken, it is advisable to use it to be certain of obtaining the proper scale.

lVe have learned that it is likely that the elevation of an aeroplane can be maintained during flight within limits of about one hundred feet, which, assuming the aeroplane to be flying at an elevation of twelve thousand feet amounts to a maximum variation in elevation of 1/120 or less than one per cent. This heing so we have thought of one mode by which the square figure can be and since late 1920 has been projected'into a square. lit the negative or copy to be cor rected be mounted parallel to the optical plane of a lens and at the same distance therefrom as originally from the plane of the lens with which the picture was taken,

the projected image of that negative when brought into tocus has, no distortion except perspective. The device we have conceived includes selection of a lens having such di-.

mensions that the distance measured along its arms from-the lens center'to itsimage plane 1s the same as. a like measin'ement in the original yiew camera. "The tocal length; oil such a lens as used in our apparatus, as;

suming Q/P to he predetermined or to be determinable by test, yields a Q substantially equalling that oi. the lens with which and when the original negative was made and as illustrated in Figures XXl and XXII. 1t

istobe understood that the symbols used in this detailed description refer to none hut the figures concerned therein, or tocertain conventional symhols, such as: P and Q used in optics as a i i ii r iqfr Og llis a line ,on photograph "WXYZ taken "so thattl is on the focal line (axis) ot the lens. P is a point on ll. To project U ll, lensrL should he so chosen, and U ll so mounted'with respect to L as to be parallel with its plane, and the distance g (or a equaling 7" (itocal length of lens of original view camera and hence assumed equal to the Q; therein involved because, in aero photography, P is so large as to he considered infinite), then the angle l lrO equals the angle termed by the axis oi the taking lens with the line through the object on the ground which P is the image; or s mply, equals l lill and also equals Pe'lfE' or equals l 'e L'lE This means that the angle made by the line. of projection of every point on the negative or copy thereof with thaairis of projection is equal to the angle made by tip line of projection from the object to theimage in the original View camera with axisor instrument; and, constitutes a direct and true reversal with angular di rnensions in true proportion to each other) of the process of taking thef'picture;

l low, it the plane represented by G'G(or G G he placed parallel to. and oriented with the terrain Whose image appears on WXYZL, and it WXYZ be placed over QHG (or; G 8 so that the perpendicular to lit) at O: intersects \E': (or E and if v (and thereforeiUOfi be-inade parallel to and oriented with the position of the sensitized surface at t e instant offtale 7 that in}. l=l) a, f" s f ing the picture; and if the lens L (so chosen be placed so that-its axis coincide with ()E (or O E and at a distance f from U0 the ratio of the projections of I oapa on G'G (or exactly proportional as to length and com parative location to the distance between the original points on the terrain which caused the images U, P and O tie, it WXYZ together withl/ and G'G' (or G G ,'namely Ue Pe, will be 69) be correctly oriented with each other with respect to the angle made by plane GGr (or G tl with 0 E (or O E the ,condition for reproduction of true proportion together with universally uniform cured. It the lens'l m is used, ,so that (m ni inlay r \p l fml a e 2 tmfl g l (or ga does not equal l, we have this conditionz Y A lllirl PLaU -'lheretore, projections hy'the lie system can not cause I r Pme'llae Pclle" q a 4 i j 7 angle gi g doesnotequal angle to equal G G be perpendicularto U h (or U E The figure obtained in this case, that is the lam system, can never be better than a rectangle which was demonstrated in connec-y tion with Figures l to V inclusive,

The word-- ob eet as used no the claims is to be construed as either the negative rcquirtive requiring correction.

It is to be ohserved that our structure permits of a turning movement about any one of three axes which intersect at right scale, minus horizontal perspective, is se' lid lOlll unless the plane. represented by "GG (or I lld mg correction orthe print from the negause angles to each other and therefore none 0t these planes may be what it will and yet necessitate adjustment, according to our scheme, of only one of the planes. Inc1den- Our ary tally our object and image planes are not required to intersect in a line which lies in the plane of the lens.

Our discovery that, in order to insure correctness under all circumstances, at least four or more points or lines on one side of an objective must be correlated by substautial superimposition with a corresponding number of points or lines on the opposite side of the objective, is one of the distinguishing features of our invention. because three points or lines are sufficient only when inspection of the object will determine the vanishing point of the horizontal perspective.

In referring to identifiable points on photographic images,it mustbe assumed that the apparent locations of objects have been substantially corrected to a single plane, either by previous approximation on the image itself or by simultaneously correcting during the process of projection.

It should be understood that the recordation need not be photographical but might be optically accomplished. indeed, conceivably even mechanically. Thus far, we have been practicing according to Figure XII Which structural arrangement happens to enable reversedalt ernative uses. In one case the control sheet 10 initially constitutes the object, the image during such first stage of the process necessarily appeal'son-the universallymovable easel. Then the light 19 is extinguished, the control sheet 10 removed, a sensitized surface substituted therefor and a target mounted on the easel becomes the object to be illuminated-from some exterior source. In consequence, during this second stage of performing our method the image becomes recorded where the control sheet 10 was first placed. According to the other alternative practice, after the control sheet 10fhas been employed where designated in Figure XII. the sensitized surface may be mounted on the universally movable easel. In short, either the object or the image may be adjusted on the universally movable easel.

We claim r 1. The combination with photographic apparatus including a sensitized surface and .a lens, of a support'inters ecting the axis of said .lens, a turntable upon said support, and an easelmounted to turn upon said turntable about two: intersecting axes.

2. The combination with photographic apparatus including'a sensitized element and a lens, a support,- a turntable movable upon said support and intersected by the axis of said lens, and an easel supported for compound movement upon said turntable so as to-include a point substantially in the axis of said lens during such compound movement.

3. Means for rectifying perspectivein a picture by photographing, comprising the combination of a camera, a universal motion support for the object to be photographed, distinct means for holding said support against motion, the arrangement being such that only one point on said support constantly lies in the axis of said lens during the universal motion.

4. The method of rectifying unknown elements of perspective in a picture, which consists in supporting the picture in the field of view of an objective, supporting at the focal plane of said objective an illuminated surface provided with a four sided figure, adjusting the plane of the picture so that four of its features as projected require only proportional change of dimension in one direction to coincide with four corners of said figure, and then photographing said picture while in such position.

5. The method of rectifying unknown elements of perspective in a photograph including four selected points. which consists in supporting the photograph in the field of view of a camera, supporting at the back of said camera an illuminated surface provided with a figure including four points corresponding in location to the four selected points in the photograph, adjusting the plane of the photograph until four of its features as projected require proportional change of dimension in only one direction to coincide with four corners of said figure, and then rephotographing said photograph while in such position.

6. The method of rectifying unknown elements of perspective in a picture, which consists-in supporting the picture and a transparent surface on which is drawn a control figure on opposite sides of a lens, said figure having not less than four sides laid out free from perspective from survey data and corners of which represent featuresidentifiable on said picture, adjusting the plane of the picture with respect to the focal plane of the lens until its selected features as projected require merely linear expansion or contraction to coincide in position with the corners on said figure, substituting a sensitized surface for said transparent surface and then photographing said picture.

7. The method of rectifying elements of perspective in a picture, which consists in holding the picture in the field of View of an objective, next correlating four points on one side of the objective by orthographic projection with four points on the opposite side of the objective, and then photograplr ing said picture.

8. The method of rectifying elements of perspective in a picture, which consists in holding an image thereof in one focal plane of an objective, next correlating four points on such focal plane of the objective by orthographic projection with four lines in the ill other focal plane of the objective, and then photographin said picture.

9. The method of rectifying elements of perspective in a picture. which consists in holding an image thereof in one focal plane of an objective, next correlating four points in the picture by orthographic projection with four lines in an illuminated sheet held in the other focal plane of the objective, then adjusting one focal plane angularly with reference to the other focal plane until an intelligible correlation occurs, and finally photographing the picture.

10. The method of rectifying unknown elements of perspective in a picture, which consists in supporting the picture in the field of view of an objective, supporting at substantially the focal plane of said objective a transparent surface provided with a plane figure, adjusting the plane of the picture so that four points on it as projected only require proportional change of dimension in one direction to coincide with four points determining a plurality of lines of said figure, and then optically recording the image of said picture while. in such position.

11. The method of rectifying unknown elements of perspective in a picture, which consists in supporting the picture in the field of view of an objective, supporting at substantially the focal plane of said objective a transparent surface provided with a plane figure, adjusting the plane of the picture so that four of its cardinal points as projected only require proportional change of dimension in one direction to coincide with ,four points on said figure three of which are vertex points, and then optically recording the image of said picture while in such position.

' 12. The method of rectifying unlrnown elements of perspective in a picture including four selected points, which consists in supporting the picture in the field of view of an objective, supporting a recording element marked with four points correspondconsists in supporting on opposite sides of a lens the plcture and a recording surface onwhich is drawn a control figure, said figure having not less than four points which rep resent points identifiable-on said picture, effecting a relative adjustment of the planes of the picture and of said surface until the points on one of said planes as projected require merely linear expansion or contraction to' coincide in position with the I points on the other of said planes, and then consists in supporting the picture in the field of view of an objective, supporting at the approximate focal plane of said objective an illuminated surface provided witha plane figure including four points corre sponding in location to the four selected points in the picture, and then adjusting the plane of the picture until the four cardinal points as projected require proportional change of dimension in 'only one direction to coincide with four points on lines defining said figure.

15.. The method of rectifying unknown elements of perspective in a picture, which consists in supporting the picture and a recording surface on which is drawn a control figure on opposite sides of a lens, said fig me having not less than four points which represent points identifiable on said picture, efiecting a relative adjustment of the planes of the picture and of said surface until the points on. one of said planes as projected require merely linear expansion or contrac tion to coincide in position with the points on the other of said planes and then eniploying the determined angular positions as a basis of measurement.

16. The hereindescribed method'of rectifying for perspective in a photograph, which consists in mounting an optical element, the photograph and an image recording element in definite angular andlinear relation to each other, and then selectively effecting an adjustment until four identically arranged points on the photograph and on the recording element assume the proper orthographic relationship.

17. The hereindescribed method of rectifying for perspective in a photograph, which consists in mounting an optical element the photograph and an image recording e ement along an optical trail, and then selectively effecting relative turning adjustments about three different axes until four identically arranged points on the photograph and on the recording element assume the proper orthographic relationship, and then rephotographing the photograph while held in its correctly adjusted angular posi-' tion.

18. The herein described method of reproducing sets of lines, which lie within a plane and are substantially radial to a plurality of points scattered along a line, as a 111- rality of sets of substantially parallel llnes lying within another plane, which consists intransferring data respecting such lines in the first plane to the second plane 1n such a manltld ner that four points in the first plane bear to a predetermined set of four points in the second plane at substantially mathematically continuous relationwhereby change of dimension, of the figure formed by the first four points so transferred, proportionately in each of two directions, angularly related, produces substantial orthographic delineation of the transferred points with the predetermined set of four points.

19.- The method of rectifying for perspective in the disclosure of a photograph which consists in arranging an optical element, the representation of such disclosure and an image recording element in suitable angular and'linear relation to each other, visually to record orthographic projectionof four Selected points on said photograph and image recording element respectively.

20. The hereindescribed method of rectifying for disclosed perspective -of a photograph which consists in selecting four feature points thereon, transmitting light rays from the photograph having elements of perspective and from an element disclosing four control points to record to the eye orthographic projection of the quartette of points on said photograph and element respectively.

21. The method of rectifying for unknown elements of perspective in a representation containing them, which consists in supporting in definite spatial relationship to an optical element; said representation and an element to be used as a standard for comparison and on which is pictorially shown a definitely dimensioned figure, said figure having not less than four .points which correspond to points revealed on said rep resentation, effecting a relative adjustment of the positions of the representation and of said comparing element until the points I on the representation as projected for comparison require merely uniform expansion or contraction in two directions substantial- 4 1y to achieve orthography with reference to the points on the comparing element and then employing the determined spatial positions as bases of measurement.

22. The combination with an easel of supporting mechanism including; one partadapted to turn about an axis, a second part carried by the first part and adapted to turn about an axis, and means turnably connecting said easel with said second part, said axes intersecting each other for the purpose specified.

23. In combination, a support provided with a circular opening, a turntable having a central opening, means involving an annular groove in the circumferential edge of one of said parts and including roller elements operatively mounted on the circumferential edge of the other of said parts, said roller elements adapted to travel in said groove, an open frame pivotally mounted in one direction across the opening of said turntable, and another open frame pivotally mounted in a different direction across the opening of said first mentioned frame.

24. In combination, a support provided with an opening, a turntable having a central openingand operatively mounted in the openingin said support, an open frame pivotally mounted in onedirection across the opening of said turntable, and an easel pivotally mounted in a different direction across the opening of said frame.

Signed by us this 16th day of April,

EDWIN H. CORLETT. MAX W. GARNETT. 

